U.S. patent number 5,262,952 [Application Number 07/658,859] was granted by the patent office on 1993-11-16 for slip control system for motor vehicle.
This patent grant is currently assigned to Mazda Motor Corporation. Invention is credited to Fumio Kageyama, Makoto Kawamura, Kazutoshi Nobumoto, Akira Sone, Toshiaki Tsuyama.
United States Patent |
5,262,952 |
Tsuyama , et al. |
November 16, 1993 |
Slip control system for motor vehicle
Abstract
A slip control system for a motor vehicle controls slips in
driving wheels and includes a sensor for detecting a slip ratio of
each driving wheel and a traction control system for decreasing a
slip of each driving wheel by controlling a driving force
transmitted to each driving wheel so that the slip ratio of each
driving wheel is at least equal to a predetermined desired slip
ratio when the slip ratio of the driving wheel becomes equal to the
desired slip ratio. An automatic transmission control system
controls an automatic transmission by using a first shift property
for a normal operation, and a second shift property for a traction
control operation which is adapted to determine a relative higher
speed stage. A device is provided for switching the first shift
property to the second shift property when the traction control
operation is started by the traction control system.
Inventors: |
Tsuyama; Toshiaki (Hiroshima,
JP), Nobumoto; Kazutoshi (Hiroshima, JP),
Kageyama; Fumio (Hiroshima, JP), Kawamura; Makoto
(Hiroshima, JP), Sone; Akira (Hiroshima,
JP) |
Assignee: |
Mazda Motor Corporation
(Hiroshima, JP)
|
Family
ID: |
12611538 |
Appl.
No.: |
07/658,859 |
Filed: |
February 21, 1991 |
Foreign Application Priority Data
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Feb 22, 1990 [JP] |
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2-41550 |
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Current U.S.
Class: |
701/87; 701/53;
701/56; 701/62; 477/138; 180/197 |
Current CPC
Class: |
B60W
10/11 (20130101); B60W 30/18172 (20130101); B60T
8/48 (20130101); B60W 30/1819 (20130101); B60T
8/175 (20130101); B60W 10/10 (20130101); B60W
10/06 (20130101); B60K 28/165 (20130101); B60W
10/18 (20130101); Y10T 477/69365 (20150115); F16H
61/0213 (20130101); F16H 2059/087 (20130101); F16H
2059/506 (20130101); F16H 2061/0227 (20130101); B60W
2552/40 (20200201) |
Current International
Class: |
B60K
28/16 (20060101); B60T 8/48 (20060101); B60T
8/17 (20060101); B60T 8/175 (20060101); F16H
61/02 (20060101); F16H 59/50 (20060101); F16H
59/08 (20060101); B60K 041/04 () |
Field of
Search: |
;364/426.01,426.02,426.03,424.1 ;180/197 ;74/866 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3711913A1 |
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Oct 1988 |
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DE |
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3927349A1 |
|
Feb 1990 |
|
DE |
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4038823A1 |
|
Jun 1991 |
|
DE |
|
Primary Examiner: Black; Thomas G.
Attorney, Agent or Firm: Keck, Mahin & Cate
Claims
What is claimed is:
1. A slip control system for a motor vehicle controlling slips in
driving wheels comprising:
means for detecting a slip ratio of each driving wheel;
traction control means for decreasing a slip of each driving wheel
by controlling a driving force transmitted to each driving wheel so
that the slip ratio of each driving wheel is at least equal to a
predetermined desired slip ratio when the slip ratio of the driving
wheel becomes equal to the desired slip ratio;
means for controlling an automatic transmission by using a first
shift property for a normal operation and a second shift property
for a traction control operation which is adapted to determine a
relative higher speed stage;
means for switching the first shift property to the second shift
property when the traction control operation is started by the
traction control means; and
means for prohibiting the automatic transmission from shifting up
in a predetermined time after said traction control means starts to
control the driving force.
2. A slip control system for a motor vehicle in accordance with
claim 1 in which said means for prohibiting includes means for
delaying the shifting up of the automatic transmission during the
predetermined time when said means for controlling said automatic
transmission determines the shifting up to be based on the second
shift property.
3. A slip control system for a motor vehicle in accordance with
claim 1 in which said first shift property includes a first shift
map and said second shift property includes a second shift map.
4. A slip control system for a motor vehicle in accordance with
claim 3 in which said second shift map includes no shift line from
a first stage to a second stage.
5. A slip control system for a motor vehicle in accordance with
claim 1 in which said prohibiting means includes means for delaying
the switching from the first shift property to the second shift
property in the predetermined time.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a slip control system for a motor
vehicle and, in particular, to a slip control system which includes
an automatic transmission and a traction control system which
controls a driving force transmitted to a driving wheel.
2. Description of the Related Art
There has been proposed a slip control system for a motor vehicle
as shown in Japanese Patent Laid-Open Publication No. 58-16948, No.
57-22948, No. 62-231836 and the like. When an excessive slip is
caused between driving wheels and road surfaces during starting
and/or running operations, the slip control system decreases the
excessive slip under a predetermined value to obtain driving forces
which are transmitted to the road surfaces from the driving wheels
and to obtain an optimal friction force between the driving wheels
and the road surfaces. As a result, not only the starting and
accelerating abilities but also the running and driving stabilities
are improved.
The slip control system includes a traction control system. The
traction control system includes an engine control system which
decreases a degree of an opening of a throttle valve, delays an
ignition timing, and cuts the supplying of fuel to the engine so as
to decrease an excessive engine output, and/or a brake control
system which increases brake fluid pressure so as to increase a
braking force of driving wheels transitionally. When the vehicle is
running on a low friction coefficient road surface, an excessive
depression of the acceleration pedal causes an excessive slip in
the driving wheels. At this time, the traction control system
obtains a desired friction coefficient between the driving wheels
and the road surfaces by decreasing the driving torque transmitted
to the driving wheels. As a result, the traction control system
decreases the excessive slip under a predetermined desired
value.
However, when the driving torque is started to be decreased by the
abovementioned slip control system, a responsibility of the driving
torque to the accelerator operation is increased. As a result,
there is a problem that a driver is not able to operate an
accelerator easily.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a slip
control system for a motor vehicle in which a driver is able to
operate an accelerator easily when the driving torque is started to
be decreased by the traction control system.
It is another object of the invention to provide a slip control
system for a motor vehicle in which the slip of the driving wheel
can be prevented from increasing immediately after the traction
control system starts to decrease the driving force.
According to one aspect of the present invention, there is provided
a slip control system for a motor vehicle controlling slips in
driving wheels comprising means for detecting a slip ratio of each
driving wheel, traction control means for decreasing a slip of each
driving wheel by controlling a driving force transmitted to each
driving wheel so that the slip ratio of each driving wheel is at
least equal to predetermined desired slip ratio when the slip ratio
of the driving wheel becomes equal to the desired slip ratio, means
for controlling an automatic transmission by using a first shift
property for a normal operation and a second shift property for a
traction control operation which is adapted to determine a relative
higher speed stage, and means for switching the first shift
property to the second shift property when the traction control
operation is started by the traction control means.
According to another aspect of the present invention, there is
provided a slip control system for a motor vehicle controlling
slips in driving wheels comprising means for detecting a slip ratio
of each driving wheel, traction control means for decreasing a slip
of each driving wheel by controlling a driving force transmitted to
each driving wheel so that the slip ratio of each driving wheel is
at least equal to predetermined desired slip ratio when the slip
ratio of the driving wheel becomes equal to the desired slip ratio,
means for controlling an automatic transmission by using a first
shift property for a normal operation and a second shift property
for a traction control operation which is adapted to determine a
relative higher speed stage, means for switching the first shift
property to the second shift property when the traction control
operation is started by the traction control means, and means for
prohibiting the automatic transmission from shifting up in a
predetermined time after said traction control means starts to
control the driving force.
The above and other objects and features of the present invention
will be apparent from the following description by taking reference
with accompanying drawings employed for preferred embodiments of
the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general diagram of a slip control system in accordance
with the present invention.
FIG. 2A is a shift map for the normal operation and FIG. 2B is a
shift map for the traction control operation.
FIG. 3A through 3D are schematic views showing the operation of a
throttle opening control mechanism.
FIG. 4 is a time chart showing an outline of the slip control.
FIG. 5 is a block diagram showing a circuit which determines a
desired slip value for the brake control operation and a desired
slip value for the engine control operation to set both desired
slip values of the rear wheels.
FIG. 6 is a diagram showing the lower limit of the throttle opening
determined by the traction control system.
FIG. 7 is a flow chart showing a procedure of prohibiting from
shifting up by a slip control unit UTR.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown a motor vehicle A having a slip
control system in accordance with an embodiment of the present
invention. The vehicle A has right and left front wheels 1FR, 1FL
for driven wheels, and right and left rear wheels 1RR, 1RL for
driving wheels.
A driving system includes an engine 2 disposed in the front portion
of the vehicle, an automatic transmission 3 connected directly to a
crankshaft of the engine 2, a propeller shaft 4 connected to an
outputshaft of the automatic transmission 3, a differential 5
connected to the rear end portion of the propeller shaft 4, and
driving shafts 6R, 6L extending from the differential 5 to right
and left directions respectively and connected to the right rear
wheel 1RR and the left rear wheel 1RL respectively.
A throttle valve 42 is provided in an intake path 41 of the engine
2 to control the amount of the intake air. The throttle valve 42 is
connected to an acceleration pedal 43 through a throttle opening
control mechanism 44 and an acceleration wire 112a. The throttle
opening control mechanism 44 includes a motor 106 which decreases
the opening of the throttle valve 42 transitionally.
The automatic transmission 3 comprises a torque converter 11 with a
lockup clutch 11A operated by hydraulic pressure and a transmission
12 with a multiple-stage transmission gear mechanism. The
transmission control operation is carried out by selecting
combinations of magnetization and/or demagnetization of a plurality
of solenoids 13a which are incorporated in a hydraulic control
circuit for the automatic transmission 3. Connection and
disconnection of the lockup clutch 11A is carried out by selecting
magnetization or demagnetization of a solenoid 13b which is
incorporated in the hydraulic control circuit.
The motor vehicle A includes a brake system. The brake system
include brakes 21FR, 21FL, 21RR, 21RL provided respectively in
wheels 1FR, 1FL, 1RR, 1RL, a tandem type master cylinder 27
connected through respective calipers (brake cylinder ) 22FR, 22FL
of the front wheel brakes 21FR, 21FL and brake conduits 23FR, 23FL,
a hydraulic booster 26 connected through respective calipers 22RR,
22RL of the rear wheel brakes 21RR, 21RL and brake conduits 23RR,
23RL, and a brake pedal 25.
The master cylinder 27 supplies predetermined brake fluid pressure
to the front wheels 1FR, 1FL. The master cylinder 27 changes the
braking force which is applied to the brake pedal 25 and boosted by
the booster 26 into the brake fluid pressure and then supplies the
brake fluid pressure to the calipers 22FR, 22FL through brake
conduits 23FR, 23FL connected respectively to first discharge
outlet 27b and second discharge outlet 27a.
The brake conduits 23FR, 23FL include relief conduits 38FR, 38FL
respectively whose end communicates to a reservoir 31. The relief
conduits 38FR, 38FL include normal closed type magnetic
proportional switching valves 37FR, 37FL which work as an outlet
valve of an antilock braking system (ABS ). FIG. 1 shows the
condition that the switching valves 37FR, 37FL are switched to the
full-closed positions.
The booster 26 boosts the braking force of the brake pedal 25 and
transmits it to the master cylinder 27, and supplies brake fluid
pressure in a booster chamber (not shown ) to the calipers 22RR,
22RL through respective brake conduits 23RR, 23RL to which an
accumulator (not shown ) is connected. A pump 29 is connected to
the booster 26 through a fluid pressure suppliing conduit 28. The
pump 29 supplies the fluid in a reservoir 31 at a predetermined
pressure to the conduit 28, which is maintained at a predetermined
line pressure by the accumulator. A return conduit 30 is connected
to the booster 26 so as to return the fluid from the booster 26 to
the reservoir 31.
The booster chamber of the booster 26 is connected to a brake
conduit 33 in which a normal opened type magnetic switching valve
34 is provided and a one way valve 35 is provided in parallel to
the switching valve 34. FIG. 1 shows the condition that the
switching valve 34 is switched to the full-opened position.
The brake conduit 33 branches into brake conduits 23RR, 23RL for
the rear wheels 1RR, 1RL at a junction point P. A normal opened
type magnetic proportional switching valve 36R is provided in the
brake conduit 23RR and a normal opened type magnetic proportional
switching valve 36L is provided in the brake conduit 23RL. The
brake conduit 23RR, 23RL are provided respectively with relief
conduits 38RR, 38RL which are branched on the down stream portion
of the switching valves 36R, 36L and communicate to the reservoir
31 respectively. The relief conduits 38RR, 38RL are provided with
normal closed type magnetic proportional switching valves 37RR,
37RL respectively which work as an outlet valve of an antilock
braking system ( ABS ). FIG. 1 shows the condition that the
switching valves 37RR, 37RL are switched to the full-closed
positions.
At the junction point P, there is provided a branch conduit 28a
communicating to the conduit 28. The branch conduit 28a is provided
with a normal closed type switching valve 32. FIG. 1 shows the
condition that the switching valve 32 is switched to the
full-closed position.
The motor vehicle A further includes a control unit UAT for the
automatic transmission 3, a slip control unit UTR which includes an
antilock braking control system (hereinafter called ABS control
system ) and a traction control system. The solenoids 13a, 13b are
controlled by the control unit UAT for the automatic transmission
3. When the brakes are operated, the ABS control system maintains
desired friction force between each wheel 1FR, 1FL, 1RR, 1RL and
the road surface to obtain the optimal braking force for the
vehicle. When the excessive slip is caused in the rear wheels 1RR,
1RL when the vehicle is being run or started, the traction control
system decreases the amount of excessive slip so as to obtain the
desired driving force of the rear wheels 1RR, 1RL.
The control unit UAT for the automatic transmission receives
detected signals from sensors 61, 62 in which the sensor 61 detects
the opening of the throttle valve 42 and the sensor 62 detects the
vehicle speed based on the rotation number of the propeller shaft
4. In accordance with these signals and stored transmission
characteristics and lockup characteristics, the control unit UAT
determines the transmission and lockup conditions, and then outputs
the control signals to the solenoids 13a, 13b of the automatic
transmission 3 to carry out the transmission and lockup
controls.
FIG. 2A is a shift map for the normal operation and FIG. 2B is a
shift map for the traction control operation.
Referring to FIGS. 2A and 2B, the control unit UAT for the
automatic transmission memorizes both the shift map for the normal
operation shown in FIG. 2A and the shift map for the traction
control operation shown in FIG. 2B. In the shift map for the
traction control operation, in order to shift up at an early stage,
a shift line between a first stage and a second stage is deleted
and respective shift lines are offset toward the low speed
direction. During the traction operation, the shift map for the
nomal operation (hereinafter called a first shift map ) is switched
to the shift map for the traction control operation (hereinafter
called a second shift map ), and a shift determination is carried
out based on the shift property in the second shift map.
To the slip control unit UTR are input various kinds of signals
which are detected respectively by the throttle sensor 61, the
vehicle speed sensor 62, wheel rotation speed sensors 63, 64, 65,
66 for detecting the wheel rotation speed of each wheel 1FR, 1FL,
1RR, 1RL, an acceleration opening sensor 67 for detecting the
depression amount of the pedal 43, a motor rotation amount sensor
68 for detecting the rotation amount of the motor 106, a steering
sensor 69 for detecting the angular steering amount of a steering
wheel (not shown ), a manual switch 70 for selecting control modes,
a brake switch 71 for detecting the depression of the pedal 25, and
a G sensor 73 for detecting a reduction speed of the vehicle.
The control unit UTR further includes an input interface for
receiving the signals from the abovementioned sensors, a
microcomputer comprising a ROM in which control programs and
various kinds of control maps and the like are stored, a RAM in
which various kinds of memories necessary for carrying out the
control are stored, a CPU, an output interface for outputing
control signals to the control unit UAT, and control circuits for
operating the valves 32, 34, 36R, 36L, 37FR, 37FL, 37RR, 37RL and
the motor 106.
In the control unit UTR, the ABS control system detects slip
conditions of each wheel 1FR, 1FL, 1RR, 1RL based on the difference
between an estimated vehicle speed and the wheel rotation speed of
each wheel detected respectively by each sensor 63, 64, 65, 66. The
estimated vehicle speed is computed based on the reduction speed of
the vehicle detected by the G sensor 73. When the ABS control
system determines that any one of the wheels 1FR, 1FL, 1RR, 1RL is
in the lock condition, the system controls the openings of the
switching valves 37FR, 37FL, 37RR, 37RL and decreases the line
fluid pressure in the brake conduit(s) 23FR, 23FL, 23RR, 23RL each
wheel of which is determined to be in the lock condition so as to
cancel the lock condition. For example, in the braking operation,
the ABS control system detects the excessive slip in the front
wheel 1FL and then carries out a duty control on the switching
valve 37FL so as to increase the opening of the switching valve
37FL so that the fluid pressure in the brake conduit 23FL and the
caliper 22FL is decreased, and then the brake fluid pressure in the
brake 21FL is decreased transitionally. The slip in the front wheel
1FL is controlled so that the front wheel 1FL is able to obtain
desired friction force against the road surface and an optimal
braking force.
In the control unit UTR, the traction control system carries out an
engine control and a brake control. The engine control is carried
out by controlling the rotation amount of the motor 106 in the
throttle opening control mechanism 44 to decrease the output of the
engine 2 transitionally when the excessive slip is caused in the
driving wheels (the rear wheels 1RR, 1RL ) at the time the vehicle
is being started or run. The brake control is carried out by
controlling the valves 32, 34 in open and close positions and
controlling the degree of opening of the valves 36R, 36L, 37RR,
37RL so as to control the value of the brake fluid pressure. By the
engine control operation and the brake control operation , driving
torques transmitted to the rear wheels 1RR, 1RL are decreased and
the slips in the rear wheels 1RR, 1RL are controlled.
In the engine control operation, the throttle opening control
mechanism 44 decreases the degree of the opening of the throttle
valve 42 less than the acceleration opening of the pedal 43 to
decrease the output of the engine 2.
Referring to FIG. 3A, the throttle opening control mechanism 44
will be described hereinafter with reference to FIGS. 3A.about.3D.
The throttle opening control mechanism 44 includes an acceleration
pedal side lever 112 connected to the acceleration pedal 43 through
an acceleration wire 112a, a throttle valve side lever 113
connected to the throttle valve 42 through a throttle wire 112t, an
abutting lever 114 having an abutting portion 114a for abutting on
the right side of the lever 112 and an abutting portion 114b for
abutting on the right side of the lever 113, a driving lever 111
provided to be driven to the left and to the right, the motor 106
driving the lever 111, and a stopper 123 restricting the leftward
movement of the lever 111 within a predetermined amount.
The lever 113 is biased to the right, which is the direction for
closing the throttle valve 42, by a return spring 121. Disposed
between the lever 112 and the lever 114 is a spring 116 for biasing
the abutting portion 114a to abut it on the lever 112. In the same
way, disposed between the lever 113 and the lever 114 is a spring
122 for biasing the abutting portion 114b to abut it on the lever
113. The biasing force of the spring 116 is set larger than those
of the spring 122 and the return spring 121.
The throttle opening control mechanism 44 constructed as described
above operates as follows.
First, there is a condition wherein the lever 111 abuts against the
stopper 123. In this condition, the levers 112, 113 and 114 are
made integral under the biasing force of the springs 116 and 122 as
shown in FIGS. 3A, 3b, so that the degree of opening of the
throttle obtained, hereinafter called a throttle opening, is
proportional to the degree of opening of the accelerator,
hereinafter called an accelerator opening. That is, the throttle
opening varies within a range of 0.about.100% while the accelerator
opening varies within a range of 0.about.100%. FIG. 3A shows a
condition wherein the throttle opening is 0%, that is, the
accelerator opening is 0%, and FIG. 3B shows a condition wherein
the throttle opening is 75%, that is, the accelerator opening is
75%. In the condition of FIG. 3B, there remains a distance between
the levers 111 and 114, which is necessary for making the throttle
opening vary from 75% to 100%. Thus, the levers 111 and 114 abut
against each other when the throttle opening becomes 100%, that is,
the accelerator opening becomes 100%.
When the lever 111 is driven to the right by the motor 106 in the
condition shown in FIG. 2B, the lever 114 is moved to the right
against the spring 116 as shown in FIG. 3C. Thus, the throttle
opening becomes small, while the accelerator opening remains as it
is.
In FIG. 3C, the throttle opening is 0%, that is, the throttle is
completly closed, while the accelerator opening is 75%. In this
condition, the abutting portion 112b of the lever 112 abuts against
the lever 113.
When the accelerator opening is made 100% in the condition shown in
FIG. 3C, the lever 112 is moved to the left, and accordingly the
lever 113 is moved to the left by the abutting portion 112b. Thus,
the throttle opening changes from 0% shown in FIG. 3c to 25% shown
in FIG. 3D.
As is clearly understood from the above description, even if the
lever 111 becomes stuck in the condition shown in FIG. 3C, the
throttle valve 42 can be opened to an opening of 25% by making the
accelerator opening 100%, so that the vehicle A can be driven to a
repair shop.
In the brake control operation, by the switching valve 34 being
switched to the full-closed position, and the switching valve 32
being switched to the full-opened position, the fluid pressure
supply conduit 28 increases the line pressure in the brake conduits
23RR, 23RL, and then the line pressure is manintained by the
switching valves 36R, 36L being switched to the closed position, or
the line pressure is released by the switching valves 37RR, 37RL
being switched to the open position.
FIG. 4 is a time chart which shows a relationship between the
general vehicle wheel rotation characteristic of the rear wheels in
the traction control operation, and the engine control operation
and brake control operation by the traction control system. FIG. 5
is a block diagram showing a circuit determining a desired slip
value for the brake control operation and a desired slip value for
the engine control operation to set both desired slip values of the
rear wheels. FIG. 6 is a diagram showing the lower limit of the
throttle opening determined by the traction control system.
FIG. 4 shows the general vehicle wheel rotation characteristic of
the driving wheel, for example rear left wheel 1RL, in the traction
control operation. The other driving wheel or rear right wheel 1RR
has substantialy the same characteristic as the rear left wheel
1RL.
In FIG. 4, V.sub.KRL shows the wheel rotation speed of the driving
wheel or the rear left wheel 1RL in the slip control operation, and
V.sub.J shows the wheel rotation speed of the driven wheel or the
average value of the front wheels 1FR, 1FL. And a threshold a and a
threshold b are shown. The threshold a corresponds to a basic
desired slip ratio SE employed in the engine control operation
which controls the slip ratio of the rear wheel 1RL by controlling
the opening of the throttle valve. The threshold b corresponds to a
basic desired slip ratio SB employed in the brake control operation
which controls the slip ratio of the rear wheel 1RL by controlling
the pressure of the brake fluid. The threshold b is set as a larger
value than the threshold a.
The slip ratio S.sub.RL of the rear wheel 1RL is calculated as
follows: ##EQU1##
The basic desired slip ratios SE, SB are calculated respectivly as
follows: ##EQU2## where SET and SBT show respectivly a desired slip
value for the engine control operation and a desired slip value for
the brake control operation, both of which are set in the rear
wheels 1RL, 1RR equally.
The desired slip value SET for the engine control operation and the
desired slip value SBT for the brake control operation are set so
that the rear wheels 1RL, 1RR obtain the predetermined driving
force mainly when the vehicle is running straight. Specifically the
desired slip values SET and SBT are determined based on parameters
such as the maximum friction coefficient .mu.max of the road
surface, the vehicle speed, the accelerator opening, the steering
angle, and the running mode selected by the mode selecting switch
70 as shown in FIG. 5.
As shown in FIG. 5, the control unit UTR has a map where a basic
value STBO of the desired slip value SBT and a basic value STAO of
the desired slip value SET are stored respectivly. Their parameters
is a maximum friction coefficient .mu.max of the road surface which
is estimated based on the larger of the slip ratios S.sub.RL or
S.sub.RR of the respective rear wheels and the driving wheel
rotation speed V.sub.J. In the map, the basic value STBO is set as
a larger value than the basic value STAO. Abovementioned desired
slip values SET and SBT are obtained respectively by multiplying
the basic values STAO, STBO by a correction gain KD. The correction
gain KD is obtained by multiplying a gain coefficient VG by gain
coefficients ACPG, STRG, MODEG. The gain coefficient VG is provided
so as to obtain the stability of the vehicle in accordance with the
increase of the vehicle speed and is given by a map 82 as a
function of the vehicle speed. The gain coefficient ACPG is
provided so as to obtain the driving force in accordance with the
acceleration demand of the driver and is given by a map 83 as a
function of the accelerator opening. The gain coefficient STRG is
provided so as to obtain the stability of the vehicle in the
steering operation and is given by a map 84 as a function of the
steering angle. The gain coefficient MODEG is given by a table 85
and is manually selected from two modes, i.e., sports mode, and
normal mode by the driver.
Referring back to FIG. 4, before the time t.sub.1, the slip is
small so that the throttle opening Tn is controlled under the basic
throttle opening TH.multidot.B which is proportional to the
accelerator opening by the lever 111 of the throttle opening
control mechanism 44 being maintained at the position shown in FIG.
3A and FIG. 3B. At this time, the pressure of the brake fluid
supplied to the brakes 21FR.about.21RL are decreased by switching
valves 32, 34, 36R, 36L and 37FR.about.37RL being maintained at the
normal positions respectively.
At the time t.sub.1 when the driving wheel rotation speed V.sub.KRL
increases to the threshold a of the basic desired slip ratio SE,
the engine control operation by the slip control system is started.
In the engine control operation, the traction control system in the
slip control unit UTR carries out a feedforward control so as to
drop the throttle opening down to a lower limit control value SM by
the lever 111 of the mechanism 44 being moved forwardly by the
motor 106.
Referring to FIG. 6, the lower limit control value SM of the
throttle opening is stored in a map, whose parameters are the
vehicle speed and the maximum friction coefficient .mu.max of the
road surface, and is determined based on these parameters. The
maximum friction coefficient .mu.max varies from 1 to 5 where the
smallest is equal to 1 and the largest is equal to 5. When the road
surface has relativly small maximum friction coefficient .mu.max, a
relative large lower limit control value SM is provided so as to
decrease the output of the engine 2 rapidly. And when the road
surface has a relative large maximum friction coefficient .mu.max,
a relative small lower limit control value SM is provided so as to
prevent the vehicle from stalling caused by the overreduction of
the output of the engine 2.
After the throttle opening is dropped down to the lower limit
control value SM, the traction control system carries out a
feedback control of the opening of the throttle valve 42 so that
the slip ratio S.sub.RL of the rear wheel 1RL becomes the desired
slip ratio SE for the engine control operation. The feedback
control is carried out by controlling the rotation of the motor 106
in the mechanism 44 so that the throttle opening is controlled
under TH.multidot.M as shown in FIG. 4.
Referring back to FIG. 4, after the time t.sub.1, the driving wheel
rotation speed V.sub.KRL of the rear wheel 1RL is still increasing
against the driven wheel rotation speed V.sub.J, while the engine
control is operated. At the time of t.sub.2, the driving wheel
rotation speed V.sub.KRL increases to the threshold b of the basic
desired slip ratio SB. At this time, the brake control operation of
the traction control is started so that the slip ratio S.sub.RL of
the rear wheel 1RL is equal to the basic desired slip ratio SB.
Namely, in the brake control operation, the slip control unit UTR
of the traction control system controls the switching valves 32,
34, 36RR, 36RL so that the brake fluid pressure of the brake 21RL
of the rear wheel 1RL is increased to the pressure Pn.sub.RL and
then the pressure Pn.sub.RL is maintained.
After the time t.sub.1, both engine control and brake control are
operated to decrease the slip of the rear wheel 1RL. When the
driving wheel rotation speed V.sub.KRL is decreased under the
threshold c of the basic desired slip ratio SB for the brake
control at the time of t.sub.3, the slip control unit UTR stops the
brake control operation by opening the switching valve 37RL and
decreasing the brake fluid pressure. Meanwhile the engine control
operation is still being carried out until there is no possibility
that the slip ratio S.sub.RL increases or the acceleration opening
is reduced to zero.
The wheel rotation characteristic of the rear left wheel 1RL is
described above, with reference to FIG. 4, and in the rear right
wheel 1RR, the engine control and brake control by the traction
control operation is similarly carried out based on the desired
slip ratio SE and SB in which the characterisric of the driving
wheel rotation speed V.sub.KRR of the rear left wheel 1RL is as
same as that of the rear left wheel 1RL shown in FIG. 4.
When the slip of either the rear right wheel 1RR or the rear left
wheel 1RL is increased at a early stage, the engine control
operation which is carried out equally in both rear wheels is
started at the time the slip ratio S.sub.RR or S.sub.RL of the rear
wheel 1RR or 1RL, or the average of the slip ratios S.sub.RR and
S.sub.RL is equal to the desired slip ratio SE for the engine
control. The brake contol operation is carried out in the rear
right wheel and rear left wheel independently. Therefore, when the
slip ratios of respective rear wheels 1RR, 1RL are equal to the
desired slip ratio SB for the brake control, the brake contol
operation is carried out respectively so that the brake fluid
pressure in the rear wheels 1RR, 1RL are increased and the slip
ratios S.sub.RR and S.sub.RL of the rear wheels 1RR and 1RL are
decreased under the desired slip ratio SB respectively.
When the traction control system starts the engine control
operation, the automatic transmission control unit UAT switches the
first shift map for the normal operation to the second shift map
for the traction control operation and thus the shifting up can be
carried out at an early stage.
In accordance with an embodiment of the invention, when the
automatic transmission control unit UAT determines the shifting up
of the transmission 3 based on the second shift map after the first
shift map is switched to the second shift map, the slip control
unit UAT prohibits the control unit UAT from shifting up the
automatic transmission 3 during a predetermined time.
FIG. 7 is a flow chart showing a procedure for prohibiting shifting
up by the slip control unit UTR.
Referring to FIG. 7, the slip control unit UTR outputs a signal i
showing the start of the engine control operation (shown in FIG. 1
) to the automatic transmission control unit UAT, and the automatic
transmission control unit UAT switches the first shift map for the
normal operation shown in FIG. 2A to the second shift map for the
traction operation shown in FIG. 2B based on the signal i from the
slip control unit UTR by which the control unit UAT determines the
shift stage of the automatic transmission 3 based on the second
shift map (P2 ). When the slip control unit UTR recognizes, based
on a signal i' sent from the automatic transmission control unit
UTA (shown in FIG. 1 ), that the control unit UTA has determined
the shifting up in the automatic transmission 3 (P2, P3 ), the
control unit UTR prohibits the control unit UAT from shifting up in
the automatic transmission 3 during a predetermined time by
outputting a signal i" to the control unit UTA (P4, P5 ). Then the
control unit UTR releases the signal i" for prohibiting shifting up
of the automatic transmission 3 after the predetermined time has
passed (P6 ).
Thus after the signal i" for prohibiting shifting up of the
automatic transmission 3 is released, the transmission 3 is shifted
up by outputing a signal to the solenoid 13b of the transmission 3
so that the responsibility of the driving torque to the accelerator
operation is decreased. As a result, the driver can operates the
accelerator easily.
In accordance with the abovementioned embodiment of the invention,
the increase of the slip of the rear wheels 1RR, 1RL, which is
caused immediately after the traction control system starts to
decrease the driving torque and the control unit UTA shifts up the
transmission, can be controlled or prevented.
In the abovementioned embodiment, the shifting up which is
determined based on the second shift map is prohibited during the
predetermined time. However, the switching of the first shift map
to the second shift map in the automatic transmission control unit
UTA may be prohibited during a predetermined time.
In the abovementioned embodiment, the slip control unit UTR
prohibits shifting up in the automatic transmission during the
predetermined time by using the abovementioned signal "i". However,
the automatic transmission control unit UAT by itself may prohibit
the switching of the first shift map to the second shift map or the
shifting up in the transmission during a predetermined time.
The present invention may be applied to a slip control system for a
motor vehicle with no ABS control system.
In the engine control operation, the engine output may be decreased
by the variable control of the ignition timing and/or the cutting
of the supplying of the fuel to the engine. Further, the
combination of this control operation in which the engine output is
decreased by the variable control of the ignition timing and/or the
cutting of the supplying of the fuel to the engine and the control
operation in which the engine output is decreased based on the
throttle opening described in the above embodiment may be
employed.
The control of the throttle valve may be carried out by the
stepping motor instead of the throttle opening control
mechanism.
Other definitions of the slip ratio may be employed if they
correspond to the abovementioned slip ratio substantially.
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